Abstract
Trichinella spiralis infected rat carcasses were incubated for 6 weeks in several animal feeds to assess how long Trichinella can present a risk for an outbreak in contaminated feeds. In groups of 6, 24 infected target rats were placed in silage, grained barley, propionic acid-preserved feed, and also into simulated pasture conditions. Test environments were sampled after one-, 2-, 4-, and 6-week-incubations. Trichinella larvae were recovered by digestion, and their infectivity was evaluated in rats. A two-week incubation reduced the number of recovered larvae, but still after 6 weeks low numbers were isolated from all feeds except from the experimental group simulating pasture conditions. After 2 weeks storage, the larvae were infective in all storage environments. However, up to 4 weeks, they survived only in the propionic acid-fermented feed and there in small numbers with reduced reproductive capability. This indicates the possibility of farm animals to get infection from rats or other infected material being hazardously mixed with hay or other feed. If silage is stored for at least one month before use, however, the risk from this forage appears to be minimized.
Highlights
Rodents have been suspected or proven to be a source of trichinellosis for pigs and farmed wild boars (Schad et al 1987, Smith & Kay 1987, Leiby et al 1990, Gamble et al 1999, Oivanen et al 2000)
After 2 weeks of incubation, Trichinella recovered from all environments were infective (Fig. 2) but in 4 weeks only parasites from propionic acid-fermented fodder reproduced in recipient rats
Because grain and propionic acid-fermented feed were kept inside a barn, the daily temperature variation was not as great as in the shaded box, which was exposed to direct sunlight and nighttime temperature drop
Summary
Rodents have been suspected or proven to be a source of trichinellosis for pigs and farmed wild boars (Schad et al 1987, Smith & Kay 1987, Leiby et al 1990, Gamble et al 1999, Oivanen et al 2000). Pork and other pig meat products as well as carnivore/omnivore game are well recognized potential sources for human trichinellosis. All these outbreaks have raised the question of natural transmission of Trichinella to horses, or other herbivores. In Finland, sylvatic trichinellosis is highly prevalent, and domestic trichinellosis in pigs and farmed wild boars has been repeatedly reported in meat inspection during recent decades (Oivanen et al 2000, Sukura et al 2001, Oivanen et al 2002). In Finland, Trichinella infection is commonly found in rats from dumps
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